Understanding an actual ethical theory that explains why it’s bad can then help us make decisions about what to do in a situation that’s less morally obvious than “Should I punch my friend in the face for no reason?”
Compare the point Schur is developing here to what Augustine says about explaining "time":
What is time? Who can explain this easily and briefly? Who can comprehend this even in thought so as to articulate the answer in words? Yet what do we speak of, in our familiar everyday conversation, more than of time? We surely know what we mean when we speak of it. We also know what is meant when we hear someone else talking about it. What then is time? Provided that no one asks me, I know. If I want to explain it to an inquirer, I do not know. (Confessions, XI, xiv, 17; Chadwick translation)
